The present invention relates to a detector and method for detecting impurities in liquids by measuring a number and size of impurities in a liquid.
The present invention is particularly but not exclusively, concerned with the detection of impurities in high-purity water (also known as super-pure water). High-purity water is used in such fields as nuclear power generation, in the electronics industry, and in medical treatment, where it is important that the water used should have minimal amounts of organic or inorganic substances contained within it. The organic substances include, for example, soluble organic matter and insoluble microorganisms, while the inorganic substances may include soluble salts and insoluble fine particles.
The importance of using high-purity water can be seen, for example, in the context of washing of semiconductor integrated circuits. When a semiconductor integrated circuit is in water containing impurities, the impurities left on the surface of the device, may cause malfunctioning of the semiconductor integrated circuit. Thus, an increased amount of impurity in the water increases a failure rate in the produced semiconductor integrated circuits, and therefore it is desirable to use water of as high a purity as possible; however, existing techniques for determining the purity level in water, when the concentration of impurities is low, are not accurate and therefore it is difficult to predict the effect any particular water sample may have. In, for example, the Journal "Kagaku Sochi" (Chemical Apparatus), pages 81 to 84 of Jan., 1984, and "Chemical Engineering", pages 22 to 27 of Nov., 1980 methods for refining water to produce high-purity water have been proposed, wherein primary pure water is produced by filtration and by reverse osmosis, and the primary pure water is further refined by a polisher and an ultra-filter thereby resulting in high-purity water. However, since the purification methods are not 100% efficient in removing impurities, it is still necessary to determine the amount of impurities in the produced high-purity water.
In a conventional system for determining the amount of impurity present the following analysis of water at an intermediate point of a line for supplying refined water to a use point is performed. A sensor is installed in a refined water supplying pipe to detect soluble organic matter, and measurement is made by a total organic carbon (TOC) measuring instrument. Meanwhile, the soluble organic matter is similarly detected by a sensor installed in the pipe, and specific resistance is measured by an electric conductance measuring instrument, with the two measurements can be carried out on-line.
With respect to fine particles in water, a part of refined water is filtered by a filter to catch fine particles. Then, fine particles on the filter are magnified and observed by using an electron microscope so as to measure the diameter and number of the particles. Microorganisms are cultured after being caught as in the case of the measurement of fine particles, and the number of the microorganisms is measured from the colonies of the microorganisms using an electron microscope.
The measurement of fine particles and microorganisms cannot be effected on-line, and a long time and expertise are required in the measurement. For this reason, it is impossible rapidly to measure the quality of the refined water and to immediately transmit the results to the refining stage, and control the refining conditions so as to improve the water quality.
A method in which the impurities in a liquid are measured on-line by direct use of a laser is proposed in, for example, Analytical Chemistry, 45(2), 223A, 1973. However, the entire amount of impurities in the liquid cannot be measured by this proposed method. As mentioned above, the impurities contained in a liquid (in water) may include granular substances which are insoluble in water and substances dissolved in water. The granular substances may be further divided into inorganic and organic substances and the latter into microorganisms and others. The dissolved substances may also be divided into inorganic and organic substances and these two types may be further divided into electrolytes and non-electrolytes. Although the above described substances are all classified as impurities in water, it is necessary to measure all of the impurities because the above described substances are contained in high-purity water in extremely small quantities. However, substances dissolved in water cannot be measured by the laser method mentioned above.
Japanese Utility Model Publication No. 51-43086 discloses a method and apparatus for calibration of a laser particle detector by providing a gas flow containing entrained solid particles of predetermined size. A liquid containing the particles of predetermined size is injected with gas into an atomization chamber through an atomizing nozzle. Part of the atomized liquid and the gas is passed from a second nozzle into a stream of warmed gas upstream of the particle detector. The liquid evaporates in the warm gas stream to leave the particles entrained in the gas stream. The detector measures the particle size, and the measured values compared with the actual size of the particles. Atomized liquid not entering the warm gas stream returns from the atomization chamber via a drain outlet into a holding tank for the liquid to be atomized.
However, this method is not entirely accurate. Since only part of the liquid reaches the detector, it is critically important that that part must be a representative sample, which is not always the case. Furthermore, the two-part atomization and evaporation also creates the possibility of error.
The present invention seeks to provide an impurity detector, and a method of measuring impurities, which is accurate, and permits on-line operation wherein a liquid sample is atomized by injecting it with gas into a chamber, in which chamber the liquid is totally evaporated.
In accordance with advantageous features of the present invention, a liquid impurity detector is provided which includes an evaporation chamber for a liquid sample, at least one atomizer nozzle for injection of a liquid sample into the chamber with a gas, and a means for heating the liquid to effect evaporation in the evacuation chamber of all of the atomized liquid. A detector region is connected to the chamber in a substantially closed manner so that all of the gas and all of the solid impurity particles entrained in the gas due to the evaporation of the liquid passed from the chamber to the detector region, and a particle detector communicates with the detector region, with the particle detector being adapted to measure the number and size of the impurity particles in the gas.
In the accordance with further advantageous features of the present invention, a method for measuring the number and size of impurities in a liquid sample is provided, with the method including the steps of atomizing the liquid sample by injecting the liquid sample with gas into an evacuation chamber from at least one nozzle, passing the atomized liquid and gas along the chamber, with all of the liquid being evaporated in the evaporation chamber to leave solid impurity particles entrained in the gas, passing all the gas having the solid impurity particles entrained therein to a detector region, and, at the detector region, measuring the number and size of solid impurity particles in the gas by a particle detector.
Advantageously, the particle detector is a dispersed laser beam detector of the type disclosed in, for example, "Air Conditioning and Refrigeration", Jan. 1984, pages 79-81, in an article entitled "Monitoring and Measurement of Sub-micron Aerosol Particles", with the laser beam detector being capable of detecting particles having a diameter greater than 0.1 .mu.m.
The evaporation of the liquid in the chamber is preferably achieved by pre-heating the gas before it is used to atomize the liquid, and temperatures of greater than 40.degree. C., and preferably greater than 60.degree. to 70.degree. C. has been found suitable. However, it is also possible to evaporate the liquid by heating the entire chamber, by applying infra-red radiation to the atomized liquid, or applying high frequency energy to the atomized liquid to create molecular movement in the liquid.
It has been found that atomization of the liquid generally produces water droplets containing only one impurity particle, so that subsequent evaporation causes the production of a flow of discrete particles, each corresponding to one impurity, whether that impurity is based on a soluble, or an insoluble, substance present in the liquid. It then becomes possible to determine the number and size of the individual particles, thereby permitting accurate analysis of the sample.